The biggest player in this group is the exclusion for employer-sponsored health insurance, worth more than $300 billion. This is the tax-free compensation a worker enjoys when his employer pays for a portion of his health insurance policy.

Also in this group is the new premium assistance offered to low- and middle-income families under Obamacare, worth about $34 billion, according to the analysis, which was published in Tax Notes.

Housing is the next biggest category, accounting for $255 billion of the $1.4 trillion. Among the biggest players here are the mortgage interest deduction, the property tax deduction, and the tax-free treatment on the first $250,000 in capital gains ($500,000 for married couples) on the sale of a home.

Third up are the $160 billion in tax breaks offered for pensions and other types of income security, such as the deduction for 401(k) contributions and the tax-free treatment of Roth IRA withdrawals.

Blueprint for a more progressive tax code

And fourth in line is the $117 billion tax break on investment income -- namely, capital gains and dividends, which are often taxed at a lower rate than ordinary income.

All told, the top 4 categories of tax expenditures account for more than 60% of the $1.4 trillion in forgone revenue.

And that $1.4 trillion is the equivalent of nearly half of the total federal revenue the government is likely to collect this year.